OBSERVATIONS ON BIOLOGICAL VARIATIONS IN CALLOSOBRUCHUS MACULATUS (F.) (COLEOPTERA: CHYRSOMELIDAE: BRUCHINAE) INFESTING STORED COWPEA IN SELECTED MARKETS OF SOUTHWEST NIGERIA

Abstract

Ecological and geographical locations have been implicated in the infestation ability of bruchid beetles. Therefore, this study were conducted to determine biological variations in the populations of C. maculatus infesting cowpea seeds in selected markets of five cities (Lagos, Akure, Ibadan, Ogbomoso and Ikole) in Southwest Nigeria. The experiment was carried out at the Department of Crop, Soil and Pest Management in the Federal University of Technology Akure (FUTA) under the ambient laboratory conditions of 27°C - 30°C and 65 – 75% relative humidity. Seeds of cowpea infested with C. maculatus were collected from five markets in Southwest Nigeria. C. maculatus derived from these seed lots were re-cultured on Oloyin cowpea seeds to provide enough adult insects for the experiments. Hundred grammes of clean uninfested Oloyin cowpea seeds were infested with 50 pairs of adult C. maculatus to determine the response of the C. maculatus from different locations on the cowpea seeds. A similar experiment was also set up to determine the effects of intraspecific effectsof competition on the traits of the C. maculatus populations. To test for preference by the C. maculatus, 100 g of the legumes (Bambara and Pigeon Pea) were provided for infestation in a no choice test. The results from this study showed that C. maculatus from all the locations infested and caused varying losses on the Oloyin cowpea seeds presented. The C. maculatus derived from infested cowpea from Ikole Ekiti had significantly (p<0.05) higher number eggs laid (1946) and emerged adult (408) compared with that from Ibadan (247 and 187 respectively). Weight of female C. maculatus from Ibadan (0.039 mg) was significantly higher than female from other locations. Across all locations, females were significantly (p<0.05) heavier than males. As the number of eggs increased the number of emerged adults also increased and consequently leads to increased weight loss. The study also showed that all the three legume crops served as host to the C. maculatus as they breed through on their seeds. However, cowpea was the most preferred among the legume type while the pigeon pea was the least. Significantly more eggs were laid on cowpea seed from which the highest number of adults also emerged particularly from C. maculatus derived from infested cowpea seeds from Ikole. The weight of both male and female were also affected by the legume type. C. maculatus that emerged from cowpea seeds were significantly heavier than those from the other seeds of legume types. The study therefore concludes that biological variation exists among populations of C. maculatus from the studied locations and they were able to infest seeds of other legumes. The studies thus recommend treatment of cowpea and other legumes seeds in these locations for protection against infestation by C. maculatus.